A Geiger counter sits on a map on which the earthquake and tsunami-crippled nuclear power plant and zones around it are marked, at an area where evacuees are screened for possible radiation before entering a shelter in Fukushima, northern Japan April 4, 2011.

OSLO (Reuters) - New ways need be found to communicate to the public the true risks of radiation from crises like the one at Japan's Fukushima nuclear plant without fanning overblown fears of an "apocalypse", scientists say.

Communication has to get across statistics about risks and at the same time address peoples' real fears, especially when they concern atomic power which has associations with the Cold War and the 1945 bombings of Hiroshima and Nagasaki.

Many experts say Japan's March 11 tsunami, which has so far left 28,000 people dead or missing, is likely to have a greater impact on public health in Japan than radiation leaking from the stricken plant.

Part of the problem is that many scientists are giving both good news and bad news -- and that can sound contradictory. They admit they find it hard to express risks in a way that can guide both governments and individuals.

"On the one hand, scientists are saying 'yes, it is very severe,'" said Jim Smith of the University of Portsmouth and an expert on the 1986 Chernobyl nuclear disaster. "On the other, I personally don't expect the health effects to be very severe from the radiation."

As an illustration of the problem between personal and public reactions, the risk of a person living in a developed nation getting cancer is about one in three over a lifetime.

A dose of 170 millisieverts -- a level found on two workers exposed to radiation at the plant and taken to hospital -- might raise the risk of getting cancer by about 1 in 100.

Yet in coming decades, millions of people in Japan who develop cancer are bound to wonder if they might have prevented it by moving further from Fukushima. So for peace of mind, getting away altogether may make sense even when risk levels are tiny. On the other hand, the stress of uprooting a life and family to move elsewhere may have a greater health impact.

Studies of previous nuclear accidents have found the psychological impact of anxiety about radiation, and the rush to try to get away from it, is very real.

And scientists presenting a study on heart attack rates in the years after the devastation of Hurricane Katrina in the United States say there may be lessons for Japan, where anxiety about radiation may add to psychiatric problems.

The U.N. Scientific Committee on the Effects of Atomic Radiation reckons that the average dose from the 1986 Chernobyl disaster in contaminated areas of the former Soviet Union works out as equivalent to a CT medical scan in a hospital.

Those doses "should not lead to substantial health effects in the general population," it said.

It said there have been 6,000 thyroid cancers among people under 18 at the time -- an unusually high number. Another U.N. report estimated that Chernobyl might eventually cause 4,000 to 9,000 deaths from cancers. Greenpeace, which opposes nuclear power, has estimated 93,000.

Little surprise then that people get confused and find reason to doubt almost all information.

In the case of Fukushima, many Japanese doubt the government; some scientists who say the health risks are slight have been denounced as stooges of the nuclear industry; and environmentalists may want to exaggerate risks as part of wider campaigns against nuclear power.

"We worry about things where we don't trust the authorities. The nuclear industry has a long legacy of being fairly secretive since it grew out of the Cold War," said Nicholas Pidgeon, a professor of psychology at Cardiff University in Wales.

NEAR COMPARISONS

But experts should still try to get risk message across.

"Don't be afraid to use statistics," said Pidgeon, noting as an example that people fleeing Japan might be exposed on an intercontinental flight to doses of solar radiation higher than those they might have received by staying put.

Talking about less closely related risks, such as the risk of dying from smoking or driving, is less convincing, he said.

R. Rajaraman, an Indian nuclear scientist, said Fukushima was "an industrial disaster but not a 'nuclear apocalypse'". German Chancellor Angela Merkel is among politicians who has referred to it as an "apocalyptic event".

"All these fears are grossly exaggerated," he said, even with bad news from Japan almost daily about the reactors.

And there are also disputes among scientists.

Japan has rated the worst reactors at Fukushima as level 5 accidents on a 1 to 7 scale where 7 is the worst. Helmut Hirsch, a scientist commissioned by environmental group Greenpeace, has rated them as 7s -- on par with the Chernobyl accident.

The crisis, and disentangling science from emotion, will complicate efforts to assess nuclear power amid competition from renewables, said Johan Rockstrom, head of the Stockholm Resilience Centre which assesses risks to the environment.

"It appears ... there is a politically driven agenda here that seems to go far beyond what science would recommend," he said of some of the reactions.

And there are wider questions about communicating risks.

"There is always a gap between a scientific assessment and how you react as a human being. People don't always trust the information they get," said Rasmus Klocker Larsen, a tsunami expert at the Stockholm Environment Institute.

Parts of south east Asia, for instance, installed sirens after a disastrous tsunami in 2004. But he said many people don't run when sirens sound, judging there is a bigger risk that it is a false alarm, and that their homes may be robbed if they leave.

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